Check Engine Light Stays on! 81'

[cheftl13]

Need a little assistance. I have an 81' corvette. When the car is off the check engine light stays lit, causing my battery to dye. When i start the car, the light turns off. Any suggestions or reasoning.

 

[gsimpson9981]

the power for the check engine bulb comes from the computer (ecm) behind seat . power is fed at term "G" which is a brown wire with white stripe. the vulp circuit is grounded when the ignition switch is turned to on or start. this lights the bulb. after a few seconds, if the computer is happy, the output to the bulb is switched off. If you dont have an 82 service manual, I would get one. They are a very valuable tool, especially for finding electrical problems. The wiring diagrams are in the book, as well as explainations of how the system operates. You can find them on ebay, used, or from the corvette suppliers new. Until you are able to find the problem, I would put a disconnect switch on the battery. They are only about $10, and will prevent your battery from being drained. Keep in mind, if the problem is in your ignition switch, you could begin to have starting issues. The only other thing I can think it could be is either a bad computer (get a rebuilt one), or the wire leading from teh check engine bulb to the ignition switch is grounded, like having a bare spot rubbed on wire. This would cause the bulb to be on anythime the computer didnt tell the bulb to go out. Which would be anytime the engine isnt running. Try this: ground the diagonistic terminal. Under the ashtray, there is a female connector looking straight up. on this connector, there is a divot cut into the plastic between the first and second connector terminals. make an 180 bend in a piece of wire and stick the bare ends into the two connectors. This should be on the right side of the connector, unless someone has turned it 180. Thats what the divot is there to help idintifing. While holding the wire into the connector, turn the key to "ON", dont start. See if the light starts flashing code 12 (flash.....flash,flash) If it does, I would say the problem is in the ignition switch or the wire from the light to the ignition switch. hope this helps

 

[jforte]

I was discussing this same thing yesterday with another Vette buddy, he had indicated it was the O2 sensors. Does anyone else agree?

 

[chevyaddict]

I'm having a battery drain as well but haven't a clue where or how its happening. Tell me more about this battery switch? Is it something that is just installed in the middle of the positive terminal lead?

 

[LVMYVT76]

It goes inline with the battery cable, usually the positive side. Most corvette supply companies sell them, O'reilly parts sells the top mount style, probably can order the side mount style.

 

[gsimpson9981]

the battery switch needs to be attached to the neg. post. its bare metal and could arc if on the positive. it bolts to the battery terminal and the cable attaches to the switch. it has a plastic knob that turns about 1/2 turn to disconnect.

 

[gsimpson9981]

the o2 sensor will make the check engine light come on. you need to check the codes for sure. But, none of the sensors will make the light stay on when the ignition is off. a bad o2 sensor will cause a rich or lean condition. the computer will try to adjust the mixture control, but will throw a code if the the adjustment is at the limit of travel.

 

[Yoda]

I question the 02 Sensor causing the battery light, if what you say is correct.

Need a little assistance. I have an 81' corvette. When the car is off the check engine light stays lit, causing my battery to dye. When i start the car, the light turns off. Any suggestions or reasoning.

With the key in the off position I don't believe the 02 Sensor is active Could it be the ignition isn't completely turning off, With the key out ~ does the Battery Light come on??

With the key out of the ignition and the battery light coming on, makes me think there might be a ground in the wiring between the computer to the light or from the ignition to light or a bad connection or partial ground at the light socket..

You can remove the 02 connection and see if the light goes out.. I would have my doubts that it would, but I've been wrong many times before

Good luck finding those electrical gremlins, they're a sneaky bunch :W

Bud

 

[wishuwerehere82]

The CEL is tied to a number of systems in the car, so it depends on which of them are active when it comes on.
With the ignition turned off, it won't be the computer.
So I would start looking at the alternator.
A bad diode trio in the alternator will turn on the CEL and discharge the battery back through the alternator.

 

[gmjunkie]

The CEL is tied to a number of systems in the car, so it depends on which of them are active when it comes on.
With the ignition turned off, it won't be the computer.
So I would start looking at the alternator.
A bad diode trio in the alternator will turn on the CEL and discharge the battery back through the alternator.

Thats Exactly Right!! And it's not the light that runs the battery down!!
It's the shorted Diode in the Alternator!!
But it's a good chance it's not the trio,it very possibly could be 1 or more of the Larger Diodes with the heat sinks around them,1 of them will run a battery down in a NY second!!!

 

[Yoda]

Jessie,

I have a question for ya

Would the "Battery" light come on with the ignition Off, I thought the Battery Light circuit was only engaged when the switch was On

I have always thought that the diodes where not engaged until the key was on, :W

Educate me oh master of the boxend

Bud

 

[gmjunkie]

Jessie,

I have a question for ya

Would the "Battery" light come on with the ignition Off, I thought the Battery Light circuit was only engaged when the switch was On

I have always thought that the diodes where not engaged until the key was on, :W

Educate me oh master of the boxend

Bud

OK Bud,I'll Try!!
1. Back feeding electricity does weird things that really don't make sense!!
2.The Big Red wire on the back side of the Alternator is to the Battery and is always Hot!! (Unless the battery is completely dead!!)
3.If 1 or more of the big Diodes is bad it can do 1 of 2 things......... or Both depending if it's OPEN or Shorted!!Same with the Diode trio,but usually not as severe and the light will be so dim that you won't hardly see it!!(Not Always,but usually)
A. Run Battery voltage to ground inside the alternator and run the battery down with No evidence!
B. Back feed voltage through the regulator to the light and turn it on after the key is off!(Can also make the Amp or Battery Gauge Show Dis-charge after key is off!!

Kinda like a bad ground can cause both front or rear signal lamps to flash when you turn on the signels......... Or kill all but the Head lamps when you step on the brake at night or make a Fuel gauge go to Full with a half a tank when the lights are turned on!!
I'm no Georg Ohm But I have stayed at the Holiday Inn Express a couple times!!
Electricity will do weird things!! It's just the nature of the beast!!